I. Field
The following description relates generally to data communication and more particularly toward signal acquisition and synchronization.
II. Background
There is an increasing demand for high capacity and reliable communication systems. Today, data traffic originates primarily from mobile telephones as well as desktop or portable computers. As time passes and technology evolves, it is foreseeable that there will be increased demand from other communication devices some of which have not been developed as of yet. For example, devices not currently thought of as communication devices such as appliances as well other consumer devices, will generate huge amounts of data for transmission. Furthermore, present day devices such as mobile phones and personal digital assistants (PDAs), among others, will not only be more prevalent but also demand unprecedented bandwidth to support large and complex interactive and multimedia applications.
While data traffic can be transmitted by way of wire, demand for wireless communication is currently and will continue to skyrocket. The increasing mobility of people of our society requires that technology associated therewith be portable as well. Thus, today many people utilize mobile phones and PDAs for voice and data transmission (e.g., mobile web, email, instant messaging . . . ). Additionally, growing numbers of people are constructing wireless home and office networks and further expecting wireless hotspots to enable Internet connectivity in schools, coffee houses, airports and other public places. Still further yet, there continues to be a large-scale movement toward integration of computer and communication technology in transportation vehicles such as cars, boats, planes, trains, etc. In essence, as computing and communication technologies continue to become more and more ubiquitous demand will continue to increase in the wireless realm in particular as it is often the most practical and convenient communication medium.
In general, the wireless communication process includes both a sender and a receiver. The sender modulates data on a carrier signal and subsequently transmits that carrier signal over a transmission medium (e.g., radio frequency). The receiver is then responsible for receiving the carrier signal over the transmission medium. More particularly, the receiver is tasked with synchronizing the received signal to determine the start of a signal, information contained by the signal, and whether or not the signal contains a message. However, synchronization is complicated by noise, interference and other factors. Despite such obstacles, the receiver must still detect or identify the signal and interpret the content to enable communication.
At present, there are many conventional spread frequency modulation technologies being employed. With these technologies, the power of a narrow band information signal is spread or enlarged across a large transmission frequency band. This spreading is advantageous at least because such transmissions are generally immune to system noise due to the small spectral power density. However, one known problem with such conventional systems is that multipath delay spread begets interference amongst a plurality of users.
One of the standards rapidly gaining commercial acceptance is orthogonal frequency division multiplexing (OFDM). OFDM is a parallel transmission communication scheme where a high-rate data stream is split over a large number of lower-rate streams and transmitted simultaneously over multiple sub-carriers spaced apart at particular frequencies or tones. The precise spacing of frequencies provides orthogonality between tones. Orthogonal frequencies minimize or eliminate crosstalk or interference amongst communication signals. In addition to high transmission rates, and resistance to interference, high spectral efficiency can be obtained as frequencies can overlap without mutual interference.
However, one problem with OFDM systems is that they are especially sensitive to receiver synchronization errors. This can cause degradation of system performance. In particular, the system can lose orthogonality amongst subcarriers and thus network users. To preserve orthogonality, the transmitter and the receiver must be synchronized. In sum, receiver synchronization is paramount to successful OFDM communications.
Accordingly, there is a need for a novel system and method of expeditious and reliable initial frame synchronization.